Gas turbine engine combustors, such as those used in engines for powering aircraft, typically include coannular outer and inner combustor liners joined at their upstream ends by an annular dome for defining therein an annular combustion dome. The dome includes a plurality of circumferentially spaced carburetors for providing a fuel/air mixture into the combustor which is conventionally ignited for generating combustion gases.
Each of the carburetors includes a typical air swirler, such as a counterrotational swirler, and a fuel injector nozzle slidably supported therein. Pressurized air is channeled to the swirlers from a conventional compressor positioned upstream of the combustor and is precisely metered through the swirler and mixed therein with fuel from the nozzle for obtaining precise fuel/air ratios for efficient combustion.
The combustion gases generated in the combustor heat the combustor liners, the combustor dome, and the swirlers which results in thermal expansion thereof. Since the combustor is annular about a longitudinal centerline of the gas turbine engine, the combustor, including the dome, expands radially outwardly to an increased diameter when so heated. The combustor also expands longitudinally, or axially, and increases in length upon being heated.
On the other hand, the fuel injector nozzles typically extend from a fuel injector stem supported from a stationary outer casing. The fuel channeled through the stem and nozzles is relatively cool, and therefore, during operation of the combustor, the combustor expands at a greater rate than that of the fuel stem supporting the nozzle. Accordingly, differential movement, both radially and axially between the fuel injector nozzles and the swirlers must be accommodated for preventing undesirable stress therein while obtaining the required precise mixing of fuel and air. Similarly, as the temperature of the combustor decreases, the combustor contracts and the differential movement between the combustor and the fuel injector nozzles must also be accommodated.
One conventional means for accommodating the differential thermal movement between the fuel injector nozzles and the swirlers joined to the combustor dome includes a free floating ferrule slidably joined to the swirler for slidably receiving a respective fuel injector nozzle. More specifically, the ferrule includes a central bore disposed coaxially with the fuel nozzle for receiving and supporting the fuel nozzle in axial sliding engagement therewith. The ferrule also includes a radially extending circular flange which is conventionally slidably captured in the swirler which allows the ferrule to move radially relative to the swirler. Accordingly, upon differential thermal movement between the fuel nozzle and the swirler joined to the dome, the nozzle is free to slide in the ferrule bore axially, and is also free to translate radially with the ferrule which is free to translate radially relative to the swirler.
However, since the ferrule is free floating and therefore is allowed to translate both radially and circumferentially within predetermined limits relative to the swirler, it is subject to aerodynamic and vibratory forces during operation of the gas turbine engine and combustor. For example, the compressed airflow from the compressor is provided at a relatively high pressure compared to the combustion gases within the combustor and acts against the ferrule. Furthermore, since the gas turbine engine includes various rotating components, including the compressor rotor, vibratory excitation forces are generated which act upon the ferrule.
Accordingly, the ferrule will vibrate and rotate relative to the fuel nozzle during operation. This motion is typically undesirable since it will cause wear between the ferrule and the fuel nozzle and swirler which decreases the effective life of those components. Accordingly, the ferrule is typically provided with a radially extending tab or lug which is positioned against a complementary radially extending stop joined to the swirler so that the lug contacts the stop for preventing rotation of the ferrule during operation.
The contact area between the lugs and respective stops is relatively small and they too are then subject to wear during operation. The wear between the lugs and the stops therefore affects the useful life of the ferrule and swirler since these components must be replaced at periodic intervals in order to prevent undesirable wear thereof which might possibly liberate a lug or stop during operation which would then be carried downstream in the engine possibly causing additional damage thereto.
Furthermore, the provision of lugs and stops results in a more complex and expensive ferrule-swirler arrangement, which is compounded by the fact that a substantial number of fuel nozzles and swirlers are used in a typical combustor around the circumference of the dome. Yet further, in more advanced gas turbine engines, double dome configurations are being considered wherein two concentric outer and inner domes include respective pluralities of carburetors, thereby increasing, yet further, the number of ferrules and corresponding lugs and stops which are required.